The invention relates generally to detection and useful application of electromagnetic waves and, more particularly, to a terahertz detection assembly. The invention can be used in systems and methods for detecting terahertz radiation that has been applied to a sample or subject in connection with determining characteristics of the sample or subject.
Terahertz radiation or terahertz waves include electromagnetic waves at frequencies in the range of about 0.3 terahertz to about 3.0 terahertz. There are applications for terahertz radiation in the civil, defense, and commercial markets. For example, the capability of terahertz radiation to penetrate into certain materials or media such as fabrics and plastics makes this wavelength useful in surveillance technologies and in methods for detecting or imaging the characteristics of a sample or subject. (Hereinafter, any medium to which such radiation is applied will be termed the “sample.”) Terahertz radiation may also be used for the evaluation of materials, rockets, and satellite structural components.
When using terahertz radiation to evaluate materials, terahertz radiation is generated and is channeled to an emitter such that terahertz waves are propagated onto the sample being evaluated. The extent to which terahertz waves are absorbed by the sample can be ascertained by detecting the terahertz waves that move adjacent to the sample or are transmitted through some thickness of the sample material and by comparing a quantity of the detected waves with the overall terahertz radiation that was directed to the sample. A determination of the terahertz waves that are absorbed by the sample can facilitate ascertaining various characteristics of the sample. Variations in absorption, reflection and/or transmission can be resolved locally to produce images.
There are various techniques that can be used to detect the terahertz radiation after being directed at the sample. For example, terahertz radiation can be detected by sensitive bolometric methods. Coherent techniques can also be used to detect terahertz signals from sources with a known phase, such as sources wherein terahertz signals are generated using pulsed or photomixed lasers. Electro-optic sampling can also be used. This technique uses nonlinear optical crystals, along with photoconductive switching. While such techniques facilitate the detection of terahertz radiation, such techniques are not very sensitive. As a result, several sources and/or detectors for terahertz waves are needed to perform the analysis. Accordingly, known detection techniques using terahertz radiation are not efficient.